This project involves theoretical and empirical studies which aim to contribute to developing a socio-economic theory of fertility that will encompass better than current theories the concepts and empirical results of fertility research in several disciplines, especially economics and sociology, and be applicable to the study of fertility in both pre-modern and modern societies. The theoretical studies focus, among other things, on the treatment within an economics framework of preferences, costs of fertility regulation, and natural fertility. Two empirical studies are planned, one extending previous work on rural fertility in new agricultural areas in mid-nineteenth century United States and one on American fertility and labor market experience in recent decades.